Clinical Radiology (1991) 44, 23-26

The Role of Magnetic Resonance Imaging in Cystic Fibrosis D. K I N S E L L A * , A. H A M I L T O N , ' , P. G O D D A R D * , A. D U N C A N ~ and F. CARSWELL§

*Department of Radiology, Bristol Royal Infirmary, tCystic Fibrosis Research Trust ClinicalFellow, Respiratory Research Group- ~Department of Radiology and §Department of Paediatrics, Hospital for Sick Children, Bristol Magnetic resonance imaging (MRI) of the chest was performed on eight patients with known cystic fibrosis. Comparison was made with the findings on plain chest radiographs. MRI shows a greater extent of disease than that predicted by the chest films alone and clearly demonstrates peribronchiai thickening and mucoid impacted bronchi. It also distinguishes between hilar lymphadenopathy and enlarged proximal pulmonary vessels as the cause of prominent hilar shadows without the need for contrast injection. Kinsella, D., Hamilton, A., Goddard, P., Duncan, A. & Carswell, F. (1991). Clinical Radiology 44, 23-26. The Role of Magnetic Resonance Imaging in Cystic Fibrosis

Cystic fibrosis is a multisystem disease most frequently resulting in chronic pulmonary and gastrointestinal symptoms. Infection of the para-nasal sinuses is often associated. The features of cystic fibrosis on plain chest radiography are generalized hyperinflation, hilar enlargement and increased linear lung markings (Catty, 1987). The latter are due to a combination of peribronchiat thickening, mucoid impacted bronchi, atelectasis and normal pulmonary vasculature. Our study was performed to determine if M R I can more accurately determine the cause of linear lung markings and hilar enlargement than plain chest radiography.

METHOD Eight patients aged from 10 to 20 years with cystic fibrosis were studied. Six were male and two were female. Each patient was clinically stable at the time of the study and had no evidence of an acute chest infection. Chest radiography and M R I of the chest was performed on each patient on the same day. The M R I images were obtained on a Picker Vista H P 2055 0.5 T unit. The chest was imaged in the coronal plane with a slice thickness of 8-10 mm, a 256 x 256 matrix and a 38-40 cm field of view. Spin-echo pulse sequences were used in each patient to acquire the data. Repetition times (TR) varied from 500 to 1500 ms. The time to echo (TE) was 30 ms. In three patients, a Short Tau Inversion Recovery Sequence (STIR) was also performed. In two patients and also in a normal volunteer a comparison of the spin-echo pulse sequences with and without respiratory gating was made. The chest radiographs and M R I scans were assessed independently and in random order.

(a)

RESULTS All the subjects were out-patients at the time of this study. They were able to tolerate the M R I scanning without difficulty. The time of scanning for each sequence ranged from 7 to 12 minutes. Respiratory gating increased the scan time further but did reduce motion artefact. This improved the image quality particularly in Correspondence to: Dr P. Goddard, Department of Radiodiagnosis, Bristol Royal Infirmary, Marlborough Street, Bristol BS2 8HW.

(b) Fig. 1 - ( a ) Coronal Tl-weighted scans of the chest of a normal volunteer in the plane of the carina. (a) Without respiratory gating. (b) With respiratory gating. The arch of the aorta is indicated (arrow).

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Table 1 - M R I results in patients with cystic fibrosis

Case Age (years)

Peribronchial Mucoid Bronchial Hilar cuffing plugging dilatation adenopathy

1 2 3 4 5 6 7 8

+++ ++ + +++ ++ ++ ++ ++

14 20 14 14 17 10 18 13

++ +++ + ++ ++ + ++ Absent

+++ + Absent +++ + Absent Absent +

++ ++ + +++ ++ + . + ++

+ Mild; + + Moderate; + + + Severe.

the lower zones, the sub diaphragmatic regions, the chest wall and adjacent to the carina (Fig. 1). The M R I findings in cystic fibrosis are summarized in Table 1. Mucoid plugging and peribronchial thickening were clearly identified in each case. They could be readily distinguished from one another by the pattern of the high intensity M R I signals (Figs 2 and 3) and were both present in areas without marked bronchial dilatation. Hilar adenopathy was present in all the patients and is highlighted on the S T I R pulse sequences (Fig. 4). The bronchial and hilar abnormalities were more clearly identified on the M R I scans than on chest radiographs (Table 2). This was most marked in the case of mucoid plugging and hilar adenopathy. Also, the extent of the bronchial abnormalities was greater on the M R I scans for each patient. No correlation was demonstrated between the M R I findings and a clinically based scoring system of patient well-being (Schwachmann Score).

(a)

DISCUSSION This study demonstrates that M R I is more accurate than chest radiography in demonstrating both the cause and extent of bronchial disease and the degree of hilar lymphadenopathy in patients with cystic fibrosis. The M R I images in the coronal plane allow easier comparison with the chest radiograph than axial scans. Mucoid impacted bronchi are seen as high signal branching structures (Gooding et al., 1984). Their accurate identification is important due to the suggestion that mucoid impaction lasting for more than three months can result in bronchiectasis (Waring et al., 1967). This is supported by the finding of mucoid plugging in the absence of significant bronchial dilatation. Lymphadenopathy not apparent on the chest radiograph is seen on M R I scans. The enlarged hilar lymph nodes have a medium signal intensity on Tl-weighted images and show an increase in signal intensity on T2weighted images (Cohen et al., 1983). The nodes are readily distinguished from proximal pulmonary vessels which produce a signal void due to the presence of flowing blood (Gamsu et al., 1983). The STIR sequence suppresses the high signal from fat (Bydder and Young, 1985). It therefore confirms that lymphadenopathy rather than fat is the casue of the high signal perihilar structures. However, the image produced has a poor spatial resolution. Respiratory gating does improve image quality in the lower zones at the cost of an increase in scan time. The upper and mid zone predominance of the bronchial

(g)

(c) Fig 2 - (a) Chest radiograph of case 1 showing bilateral mid and upper zone linear opacification. Coronal MRI scans (TR 1500 ms; TE 30 ms) demonstrated peribronchial wall thickening in the left mid zone (b) and the right upper zone (c) where there is also marked bronchial dilatation (bronchiectasis). In (b), a thick walled bronchus (arrows) demonstrates connection between the left main bronchus and a bronchiectatic cyst (arrow-head).

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THE ROLE OF MAGNETIC RESONANCE IMAGING IN CYSTIC FIBROSIS

(a) (a)

O) (b)

Fig. 4 (a) Coronal M R I scans of case 2. The scans are in the same plane using T1 weighted (a) and STIR (b) pulse sequences. Despite poor spatial resolution the areas ofhilar tymphadenopathy are highlighted on the STIR sequence (arrows). The mucoid plugging in the left upper zone also has high signal on the STIR sequence and thus has high water content.

Table 2 - Comparison of chest radiograph and MRI findings

(c) Fig. 3 - (a) Chest radiograph of case 5 with bilateral predominantly upper zone linear opacification and prominent hilar shadows. Coronal MRI scans (TR 1500 ms; TE 30 ms) show bilateral upper zone and right mid zone mucoid plugging ((b) and (c)). This is most marked in the right upper zone (b). No enlargement of the pulmonary artery is present but enlarged nodes are seen (arrows).

Abnormality

Chest radiograph % positive

MRI % positive

Peribronchial cuffing Bronchial dilatation Mucoid plugging Hilar adenopathy

87 50 0 22

100 66 87 100

disease in cystic fibrosis allows scans of diagnostic quality to be performed without gating. Computed tomography (CT) has also been used to delineate the bronchial and hilar abnormalities in cystic fibrosis. Two studies have shown a greater extent of bronchial disease on CT scans as compared to chest radiographs (Jacobsen et al., 1986; Hansell and Strickland, 1989). CT scanning can also demonstrate pleural thickening

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(Hansell and Strickland, 1989) and is an important finding in the context o f patient suitability for heart-lung transplantation. N o n e o f the patients in this study had evidence o f pleural thickening on their M R I scans, although it would be expected that pleural thickening would have been demonstrated by M R I if it had been present. N o n e o f this g r o u p o f patients had undergone a pleurodesis. The assessment o f the beneficial effect o f therapy in cystic fibrosis by c o m p a r i s o n o f chest radiographs is difficult. This is due to the lack o f sensitivity and specificity o f the technique as well as to interfilm variation in exposure factors and patient inspiratory effort. M R I o f the chest can accurately m o n i t o r the extent o f the disease without the need for ionizing radiation. This is an important consideration in a patient g r o u p n o w growing to a d u l t h o o d and childbearing age. There is a need for a technique that monitors the condition without causing harm. The degree o f m u c o i d plugging and the n u m b e r and size o f enlarged lymph nodes are objective indicators that could be used to measure the response to different treatment protocols. At present M R I is not generally available and is used mainly by neuroradiologists. As M R I becomes m o r e widely used, its value in other areas will become apparent. Its utilization in patients with cystic fibrosis is just one example o f the i m p o r t a n t role for M R I outside the central nervous system.

Acknowledgements. We thank the staff of the Magnetic Resonance Imaging Centre, Frenchay Hospital, Bristol, and Mrs K. Creed for typing the manuscript.

REFERENCES

Bydder, GM & Young, IR (1985). Magnetic Resonance Imaging: clinical use of the Inversion Recovery Sequence. Journalof Computer Assisted Tomography, 9, 659-675. Carty, H (1987). The chest radiograph in cystic fibrosis in children. Journal of the Royal Society of Medicine, Supplement No. 15, 80, 38 46. Cohen, MD, Creviston, S & LiPuma, JP (1983). Nuclear magnetic resonance evaluation of hilar and mediastinal lymphadenopathy. Radiology, 148, 739-742. Gamsu, G, Webb, WR, Sheldon, P, Kaufman, L, Crooks, L, Birnberg, FA, Goodman, P, Hinchcliffe, W & Hedgecock, M (1983). Nuclear magnetic resonance imaging of the thorax, Radiology, 147, 473-480. Gooding, CA, Lallemand, DP, Brasch, RC, Wesbey, GE & Davis, B (1984). Magnetic resonance imaging in cystic fibrosis. Journal of Paediatrics, 105, 384-388. Hansell, DM & Strickland, B (1989). High resolution computed tomography in pulmonary cystic fibrosis. British Journal of Radiology, 62, 1-5. Jacobsen, LE, Houston, CS, Habbick, BF, Gernereux, GP & Howie, JL (1986). Cystic fibrosis: a comparison of computed tomography and plain chest radiographs. Journal of the Canadian Association of Radiology, 37, 17-21. Waring, WW, Brunt, CH & Hilman, BC (1967). Mucoid impaction of the bronchi in cystic fibrosis. Pediatrics, 39, 166 175.

The role of magnetic resonance imaging in cystic fibrosis.

Magnetic resonance imaging (MRI) of the chest was performed on eight patients with known cystic fibrosis. Comparison was made with the findings on pla...
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